The present invention relates to a chemical-mechanical polishing apparatus, and particularly to a chemical-mechanical polishing apparatus characterized by a polishing cloth.
Recently, along with higher integration of semiconductor devices, it has been increasingly required to improve a technique for finely processing the semiconductor devices. To form a fine pattern of a photoresist which is essential to the above technique for finely processing semiconductor devices, studies have been extensively made to develop a photoresist having a high sensitivity and a high resolution and also to develop a high resolution exposure system. However, if a surface of a film to be processed is not flat, a photoresist within an exposure region cannot be accurately, finely patterned owing to a relationship between the flatness of the film surface and a focal depth of the exposure system and/or the performance of the photoresist.
Not only to meet the requirement for the above-described fine processing, but also to meet a requirement for step coverage of a film to be processed such as an interconnection film formed on an underlaying layer being not flat, it has been required to develop a technique for planarizing the surface of the underlying layer formed under the film to be processed, and a CPM (Chemical-Mechanical Polishing) process has been known as a preferable planarization technique.
An apparatus used for planarizing a surface to be processed by the above-described CMP process is a CMP apparatus to which the present invention pertains.
First, a related art CMP apparatus and a process using the CMP apparatus will be described with reference to FIG. 4.
As shown in FIG. 4, a CMP apparatus 1 mainly includes a turn table 10, a holding base 20, a dressing plate 30, and a polishing solution supply unit 40. The turn table 10 on which a polishing cloth 12 is stuck is rotatably supported by a turning shaft 11. The holding base 20 on which a substrate to be processed such as a semiconductor wafer 22 is held is rotatably supported by a turning shaft 21 and is applied with a pressure through the turning shaft 21. The dressing plate 30, which is adapted to coarsen the polishing cloth 12, is rotatably supported by a turning shaft 31 and is applied with a pressure through the turning shaft 31.
The surface of the turn table 10 on which the polishing cloth 12 is stuck is finished at a very high flatness because it becomes a reference plane. The polishing cloth 12 is made from a hard resin such as a polyurethane resin containing small foams.
The semiconductor wafer 22 is stuck on an underside of the holding base 20 with a sticking material such as sticky wax or a wafer packing film or it is stuck on the underside of the holding base 20 by vacuum-attraction. The semiconductor wafer 22 is polished by the polishing cloth 12 stuck on the turn table 10 in a state in which the semiconductor wafer 22 is pressed on the polishing cloth 12 by a pressure applied from a polishing pressure regulator (not shown) through the turning shaft 21.
On the underside of the dressing plate 30 are fixedly bonded hard grains 32 of a hard ceramic, diamond or the like. The surface of the polishing cloth 12 is coarsened (dressed) in a state in which both the dressing plate 30 and the turn table 10 are rotated and the dressing plate 30 is pressed on the polishing cloth 12 stuck on the turn table 10 by a pressure applied to the dressing plate 30.
The polishing solution supply unit 40 is used to supply a polishing solution (slurry) on the polishing cloth 12 stuck on the turn table 10 through a leading end of a supply nozzle 41. The polishing solution contains small abrasive grains such as silica grains dispersed in an alkali solution such as aqueous ammonia.
An operation for polishing a semiconductor wafer using the CMP apparatus 1 will be described below.
First, the polishing cloth 12 stuck on the turn table 10 is dressed by rotating both the turn table 10 and the dressing plate 30, and moving down the dressing plate 30 to press the dressing plate 30 on the polishing cloth 12 stuck on the turn table 10 at a specific pressure, whereby the surface of the polishing cloth 12 is scratched with the hard grains 32 fixedly bonded on the underside of the dressing plate 30. With the dressing continued for a specific time, numberless small irregularities 12a are formed on the surface of the polishing cloth 12 due to numberless scratches, to make fuzzy the surface of the polishing cloth 12.
After the surface of the polishing cloth 12 is dressed for the specific time, the dressing plate 30 is moved up, followed by stoppage of rotation of both the dressing plate 30 and the turn table 10.
Then, the semiconductor wafer 22 is stuck on the underside of the holding base 20 with a surface to be processed downward, and a pressure to be applied from the polishing pressure regulator (not shown) to the holding base 20 is set.
The turn table 10 is rotated, and the polishing solution is supplied from the leading end of the supply nozzle 41 of the polishing solution supply unit 40 on a central portion of the polishing cloth 12 stuck on the turn table 10. The polishing solution supplied from the leading end of the supply nozzle 41 is spread over the entire surface of the polishing cloth 12 by a centrifugal force caused by rotation of the turn table 10.
The holding base 20 on which the semiconductor wafer 22 is stuck is rotated, and is moved down to press the surface to be processed of the semiconductor wafer 22 on the polishing cloth 12 stuck on the turn table 10 at a specific pressure.
In the state in which the surface to be processed of the semiconductor wafer 22 is pressed on the polishing cloth 12, the polishing solution is carried onto the surface to be processed of the semiconductor wafer 22 through the irregularities 12a formed on the surface of the polishing cloth 12, to polish the surface to be processed of the semiconductor wafer 22, thus planarizing the surface to be processed.
After the surface to be processed of the semiconductor wafer 22 is polished a specific amount, the holding base 20 is moved up, followed by stoppage of rotation of the holding base 20 and the turn table 10 and stoppage of supply of the polishing solution. Then, the semiconductor wafer 22 is separated from the underside of the holding base 20.
In this way, surfaces to be processed of semiconductor wafers 22 are sequentially planarized by repeating the above steps of sticking a semiconductor wafer 22 on the holding base 20, planarizing a surface to be processed of the semiconductor wafer 22, and separating the semiconductor wafer 22 from the underside of the holding base 20.
The result of planarizing a large number of semiconductor wafers 22 causes wear of irregularities of the polishing cloth 12. This deteriorates the performance of supplying the polishing solution on a surface to be processed of a semiconductor wafer 22, to thereby degrade a rate of planarizing the surface to be processed and to make poor the flatness. For this reason, after planarization of a specific number of semiconductor wafers 22, the polishing cloth 12 is dressed by the dressing plate 20 in the same manner as described above.
In planarization of surfaces to be processed of semiconductor wafers 22 by the CMP apparatus 1, for suppressing occurrence of micro-scratches on a surface to be processed of a semiconductor wafer 22, it is necessary to quickly remove, from the surface of a polishing cloth 12, shavings of the polishing cloth 12 and hard grains 32 peeled from the underside of the dressing plate 30 upon dressing and also large grains such as flakes of silicon produced upon planarization of the semiconductor wafer 22, and to supply a new polishing solution to the surface to be processed of the semiconductor wafer 22 pressed on the polishing cloth 12. This causes a problem that a large amount of the polishing solution is consumed, to thereby increase the production cost in fabrication of semiconductor devices.
Further, in planarization of surfaces to be processed of semiconductor wafers 22 by the CMP apparatus 1, as described above, the polishing cloth 12 must be dressed after planarization of a specific number of semiconductor wafers 22 for preventing the deterioration of the flatness of a surface to be processed upon planarization. This degrades the working ratio of planarization by the CMP apparatus 1, and also requires exchange of the dressing plate 30 because the dressing performance of the dressing plate 30 is gradually deteriorated. This causes a problem in increasing the number of works and the production cost due to exchange of the dressing plate 30.